The invention discloses a hydraulic overflow classification technology for silicon carbide. The technology comprises the steps that (1) silicon carbide mixed slurry subjected to purification treatment is driven into a classification kettle, the mass concentration of the mixed slurry is 20-30%, and a dispersing agent is added into the mixed slurry; (2) on a constant-pressure condition, the flow velocity of water is adjusted to 500 kg/h, and ultrasonic classification is carried out on products of below 2000 meshes; and (3) the flow velocity of water is adjusted to 1000-2500 kg/h, and ultrasonic classification is carried out on the products of 1000-2000 meshes. By means of the technology, it can be guaranteed that the particle size distribution of the silicon carbide is narrow, and micropowder particles are uniform.